The premierships are one thing - the other is how consistently good melbourne has been under his tenure. I agree that Bellamys coaching resume would be enhanced tom brady style if he did it at another club.
However, he has kept a club in the hunt for a premiership for nearly 20years straight - I dont recall melbourne ever having any real down years. Bennett at his peak had some down years at Brisbane. Even the mighty Raiders had a down year in 92 during there run.
I cant think of another sporting competition with a salary cap* that has seen a club stay at the top for so long.
Also for me Bennett teams at there best have individuals playing at their peak, through motivation / happiness. Thats why you see him have success in big games and rep footy.
Bellamy at his peak has systems in place to make the very most out of scrub footballers (hence why you dont buy a half back croft - if your going to buy a melbourne player you want him to have been there for a long long time) make the most out of every footballer, in every game, in every play. Hence why you have such sustained success with him.
If I could have either of them back at the raiders, I would take Bellamy in a heartbeat. For the mighty blues I would take bennett in a heartbeat. Both sides would be near unstoppable at this point with those coaches (and a new half back for the raiders- maybe you guys could send us reynolds.).